1. Field of the Invention
The present invention relates to a receptacle type optical module and a production method therefor.
2. Description of the Related Art
In an optical communication system using an optical fiber as a transmission line, a laser diode module (LD module) is used to introduce light emitted from a light emitting component (e.g., laser diode) into the optical fiber. In the LD module, the light emitting component and the incident end face of the optical fiber are fixed in a given positional relationship, and a condenser lens is interposed between the light emitting component and the incident end face of the optical fiber. In this kind of LD module, the positional relation between components has a direct effect on optical coupling efficiency, so that the components must be positioned with an extremely high accuracy as less than or equal to 1 xcexcm. Further, this positioning accuracy must be maintained for a long period of time.
The components mounted on a printed wiring board built in a communication device are generally classified into a surface mount type and a through hole mount type. A typical example of the surface mount type components is an LSI, which has a form called a flat package. Such a component is soldered to the printed wiring board by a reflow soldering process. This process is performed by printing a solder paste on the printed wiring board, making the surface mount type component stick to the printed solder paste, and heating the whole in a conveyer furnace to a solder surface temperature of 220xc2x0 C. or higher.
A typical example of the through hole mount type components is a large-capacity capacitor or a multi-terminal (200 or more terminals) LSI. The multi-terminal LSI has a terminals form called a PGA (Pin Grid Array). Such a through hole mount type component is soldered to the printed wiring board by a flow soldering process. This process is performed by inserting the terminals of the through hole mount type component into through holes of the printed wiring board, and putting the printed wiring board into a solder bath heated at about 260xc2x0 C. from the side opposite to its component mounting surface.
In mounting an optical module such as an LD module on the printed wiring board by soldering like the surface mount type component or the through hole mount type component, a so-called pigtail type optical module with an optical fiber cord is not suitable as the optical module. That is, the optical fiber cord usually has a nylon coating, and the nylon coating has a low resistance to heat at about 80xc2x0 C., so that it is melted in the soldering step. Furthermore, the optical fiber cord itself invites inconveniences in accommodation and handling at a manufacturing location, causing a remarkable reduction in mounting efficiency to the printed wiring board. Accordingly, to allow a soldering process for the optical module and reduce a manufacturing cost, the provision of a so-called receptacle type optical module is indispensable.
A surface-mount receptacle type optical module is disclosed in U.S. Pat. No. 6,181,854B1. This receptacle type optical module is produced in the following manner. An LD is mounted on an Si substrate, and a ferrule having an optical fiber is inserted in a V groove formed on the Si substrate and fixed in the V groove by an adhesive. Further, a block having a groove similar in cross section to the V groove of the Si substrate is mounted on the Si substrate so as to press the ferrule from the upper side thereof. The ferrule is fixed in the V groove of the Si substrate by applying the adhesive to the upper side of the ferrule and then curing the adhesive.
In mounting the LD, the mounting accuracy must be made to fall within xc2x11 xcexcm. The LD used in this optical module is a spot-size converted LD (SSC-LD) designed so that the spot size is reduced to attain efficient incidence of light on the optical fiber. A transparent silicone resin is applied to an optical coupling portion between the LD and the optical fiber, thereby sealing the optical coupling portion with the resin. Further, all the components are molded with epoxy resin in the condition where an end portion of the ferrule is projected from the side surface of the substrate, thus completing the optical module.
The receptacle type optical module described in the above patent has the following two problems. One of the two problems is the lack of mechanical rigidity, and the other is the use of a special-purpose LD. The receptacle type optical module is required to have a strength against pressures received in connecting and disconnecting an optical connector. Accordingly, it is difficult to maintain a sufficient strength by the molding resin, and the ferrule is therefore held between the Si substrate and the block and bonded together by the adhesive, thus reinforcing the optical module. However, the strength on the Si substrate with the V groove depends on the strength of the adhesive, and if the amount of the adhesive to be charged is not controlled, there arises a problem such that the molding resin may enter the bonded portion between the ferrule and the Si substrate.
Furthermore, the rigidity of the Si substrate is insufficient, so that the substrate may be warped by a stress in bonding the substrate to the lead frame or in molding, causing misalignment of the optical fiber and an output loss. In the optical module described in the above patent, the Si substrate is formed with a sectionally rectangular groove perpendicular to the V groove, so as to make the end face of the ferrule abut against the inner wall surface of this rectangular groove. Accordingly, the presence of this rectangular groove may accelerate the warpage of the substrate by the stress in bonding the substrate to the lead frame or in molding. Furthermore, since the LD is mounted directly on the Si substrate, whether or not the deterioration of the LD due to the mounting on the Si substrate has occurred must be evaluated after completing the optical module, so that the cost of product is largely determined by the yield in such a screening step.
It is therefore an object of the present invention to provide a receptacle type optical module having sufficient mechanical rigidity which can be produced at a low cost.
It is another object of the present invention to provide a production method for a receptacle type optical module having sufficient mechanical rigidity.
In accordance with an aspect of the present invention, there is provided a receptacle type optical module comprising a lead frame having a plurality of leads; a block mounted on the lead frame, the block having a through hole; a ferrule inserted and fixed in the through hole of the block, the ferrule having an optical fiber; a carrier mounted on the block, the carrier having a wiring pattern; an optical element mounted on the carrier; a graded index lens fixed to an end face of the ferrule, the graded index lens having a spherical end face adjacent to the optical element; and a transparent resin for sealing an optical coupling portion between the optical element and the graded index lens.
Preferably, the block has an L-shape. By using the L-shaped block with the ferrule inserted and fixed in the through hole, sufficient mechanical rigidity can be obtained to ensure a strength against pressures received in connecting and disconnecting an optical connector and in molding. Further, since the optical element is mounted on the carrier to prepare a carrier assembly, the reliability of the optical element can be evaluated in the form of the carrier assembly. Accordingly, a cost increase due to module assembly yield can be suppressed.
The optical element comprises a laser diode, for example. Preferably, the transparent resin comprises a silicone resin. Preferably, the optical module further comprises resin flow blocking means (dam) formed on the L-shaped block at a position under the graded index lens. The dam is formed of a resin having a viscosity higher than that of the transparent resin. By adding the dam, the flow of the silicone resin having a relatively low viscosity and high transparency can be prevented to thereby reliably achieve the resin sealing of the optical coupling portion.
In accordance with another aspect of the present invention, there is provided a receptacle type optical module comprising a lead frame having a plurality of leads; an L-shaped block mounted on the lead frame, the L-shaped block having a through hole; a ferrule inserted and fixed in the through hole of the L-shaped block, the ferrule having an optical fiber; a carrier mounted on the L-shaped block, the carrier having a wiring pattern; an optical element mounted on the carrier; a graded index lens fixed to an end face of the ferrule, the graded index lens having a spherical end face adjacent to the optical element; a transparent resin for sealing an optical coupling portion between the optical element and the graded index lens; and a resin molded package for encapsulating all of the lead frame, the L-shaped block, the ferrule, the-carrier, and the optical element except a part of the lead frame and a part of the ferrule.
In accordance with a further aspect of the present invention, there is provided a production method for a receptacle type optical module, comprising the steps of mounting an optical element on a carrier having a wiring pattern; connecting the wiring pattern of the carrier and the optical element by means of a first wire; performing a screening test for the optical element; preparing an L-shaped block having a through hole; press-fitting a ferrule having an optical fiber into the through hole of the L-shaped block; mounting the carrier on the L-shaped block in the condition where the optical element is mounted on the carrier; bonding a graded index lens to an end face of the ferrule after aligning the graded index lens to the optical fiber and the optical element; mounting the L-shaped block on a lead frame; connecting the wiring pattern of the carrier and the lead frame by means of a second wire; sealing an optical coupling portion between the optical element and the graded index lens with a transparent resin; and encapsulating all of the lead frame, the L-shaped block, the ferrule, the carrier, and the optical element except a part of the lead frame and a part of the ferrule in a resin molded package.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.